Flex-segmented golf club shaft and method of manufacture

ABSTRACT

A flex-segmented golf club shaft having tip and butt sections of preselected stiffness and flex characteristics, respectively, that are formed as separate pieces, with the larger butt section overlapping and fused to the smaller tip section and forming an external step in the shaft profile. An alternative embodiment has three such sections and two steps. The method of forming the shaft by wrapping a preselected tip section from a selection of available sections on a mandrel having a pronounced step, and then wrapping a preselected butt section from a selection of available sections on the mandrel in overlapping relation with the tip section, to provide optimized characteristics for a particular golf swing.

This application claims the benefit of prior copending provisional application No. 60/342,453, filed Dec. 17, 2001.

BACKGROUND OF THE INVENTION

This invention relates to composite elements that are composed of resin-impregnated laminations or plies of carbon graphite fiber or other material that is wrapped, rolled or wound into elongated usually tubular shapes, and relates more particularly to composite golf club shafts in tapered tubular form having a grip portion at one end and a tip portion at the other end for connection to a golf club head.

Composite shafts are widely used in golf clubs and are manufactured in well known, conventional ways by different manufacturers. Examples of several approaches are shown and described in U.S. Pat. Nos. 4,097,626, 5,380,389, 5,556,677, and 5,931,744. Typically, the shafts are manufactured by wrapping or rolling laminations or plies of cloth composed of graphite or other fibers and impregnated with uncured epoxy or other resin. The impregnated fabric, or “pre-preg” is wrapped onto an elongated mandrel having a tapered outside surface to produce an elongated tubular element that covers the mandrel and has a taper that follows the taper of the mandrel. It has been customary to design clubs to suit the desires of different golfers, by varying the taper, wall thickness and materials in such shafts. Fiber orientation in the plies is an important variable as well. The numbers of plies and the directions of the fibers in the plies, as well as the types of fibers used, are varied according to principles that are well known in the industry. Some plies are applied to the mandrel so that the fibers extend longitudinally of the mandrel, and thus the shaft, and others have fibers that are at angles on the mandrel ranging from zero degrees to ninety degrees with the axis, to produce different performance characteristics in the shaft. After the lay-up on the mandrel has been completed, the shaft is cured in any of several ways, sometimes covered with shrink films or in molds, and is removed from the mandrel for finishing.

Important shaft characteristics that are determined by the well known design factors include weight, overall flex, torsional strength and tip stiffness, all of which affect the shaft and its “feel” in ways that are well known in the industry. Variations in these factors produce golf clubs that perform differently in ways that are known to golf club designers and manufacturers. One of the most significant factors is tip stiffness, which is a characteristic that can change not only the trajectory of the ball but also how the club feels. This has become a predominant factor in shaft promotion and marketing. Also, overall flex long has been a recognized variable that should be matched to a particular golfer's swing, which typically vary in speed, and also in aspects that affect the “launch” angle of the ball. The present invention provides a new and different way to match the club shaft to the golfer's swing, by making it possible, and economically practical, to offer an variety of flex profiles within a general flex category by changing the tip of the shaft to distinctly different, and selected, degrees of stiffness, enabling a golfer who uses clubs with a selected level of overall shaft flex to have a selected level of tip stiffness as well.

SUMMARY OF THE INVENTION

The present invention resides in a golf club shaft, and the method of producing the shaft, that is discontinuous in construction along its length, with separately formed butt and tip segments or sections that have selected flex and stiffness characteristics and are overlapped and securely joined together at the upper end of the tip section. This enables the manufacturer to provide a selection of two or more different butt sections and a selection of two or more different tip sections and thereby to produce a golf club shaft having optimized performance characteristics for a particular golf swing.

More specifically, the shaft of the invention is produced by providing selections of tip sections and butt sections with known stiffness and flex characteristics, respectively; then producing a selected tip section by wrapping or rolling it in a conventional manner, but without the plies that will form the butt section and with a short end portion for joinder to the butt section; and then producing the selected butt section as a separate part having one end portion that is disposed around and overlaps the tip portion and is securely joined thereto by the overlapping portions when the shaft is cured in the usual manner. This shaft thus will have combined characteristics of the selected butt and tip sections, and a discrete “step,” shoulder or visible transition between the end of the butt section and the tip section. This shoulder can be shaped in different ways in the wrapping and curing process, primarily for aesthetic purposes, and the flex and stiffness selections can be provided in different weight selections as well.

An alternative embodiment of the invention provides an additional, intermediate or transition section for the butt section of the shaft, between the tip section and the extended butt section, thus providing even greater versatility by adding a selection of different intermediate sections. In all other respects, this can be accomplished in the same manner as in the preferred embodiment.

The preferred method of producing shafts in accordance with the invention uses a tapered mandrel having a discrete transition zone, or shoulder, between the smaller tip end portion and the larger butt end portion, and the plies forming the tip section are wrapped or rolled on the tip portion of the mandrel with their edges against the shoulder, which is a frustroconical portion of the mandrel that has a taper rate much greater than that of a conventional mandrel, the taper rates in the tip and butt sections being within ranges of conventional tapers in the industry. The completed tip section effectively builds up the tip portion of the mandrel substantially to the level of the butt portion of the mandrel, and the plies of the butt portion are made axially long enough to extend over the adjacent end portion of the tip section by an amount that is sufficient to form a secure connection between the two sections. When three sections are to be formed in a shaft, the process is performed first between the tip and intermediate sections and then between the intermediate section and the extended butt section.

Additional features and advantages of the invention will become apparent from the following detailed description, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a golf club having a golf club shaft in accordance with the present invention, with the external step shown slightly exaggerated;

FIG. 2 is an enlarged side elevational view of the shaft of the golf club shown FIG. 1, longitudinally compressed and not to scale;

FIG. 3 is a schematic, longitudinally compressed cross-sectional view illustrating conventional lay-up of plies on a a mandrel in the manner typically used, as prior art;

FIG. 4 is a schematic cross-sectional view similar to FIG. 3 but illustrating the primary difference in the present invention.

FIGS. 5A to 5D are fragmentary, schematic side elevational views illustrating various external configurations of the profiles of the shaft;

FIG. 6 is a schematic view similar to FIG. 4 and showing a mandrel for an alternative embodiment of the invention, having an intermediate section between the butt and tip sections;

FIG. 7 is an exploded schematic view of a mandrel for practicing the invention and a plurality of illustrative fabric wraps to be applied to the mandrel to produce the tip and butt sections;

FIGS. 8A and 8B are fragmentary schematic views illustrating the preferred sequence of formation of the tip and butt sections of the invention; and

FIG. 9 is a table showing one set of possible combinations of the tip and butt sections that can be made with an illustrative group of available selections.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in the drawings for purposes of illustration, the invention is embodied in a golf club shaft, indicated generally by the reference number 10, that is incorporated in a golf club indicated generally as 11 and having a club head 12, shown as a so-called “wood”, attached to one end, the “tip” end of the shaft and having a hand grip 13 wrapped around the opposite or “butt” end. While a “wood” configuration is shown, the invention also is applicable to shafts for other clubs.

Such shafts typically are tapered from the largest diameter at the butt end to the smallest diameter at the tip end. This shaft is of the kind known as “composite” shaft composed of resin-impregnated fabric that is composed of a plurality of laminations or plies that form an elongated tubular shaft. As has been described in general in the Background of the Invention, composite golf club shafts typically are produced by wrapping, winding or rolling plies, indicated generally as 14 in FIG. 3, of resin impregnated cloth onto a tapered tool or mandrel 15, as illustrated schematically in FIG. 3. Hereinafter, “wrapping” will be used to encompass all available ways to apply such plies. The mandrel is an elongated rod, usually composed of metal, that is longer than the shaft to be produced and has an outside surface that is shaped as desired for the inside surface of the shaft, which is approximately the same shape as the outside surface as well. Full length plies 14 are wrapped successively around the mandrel until the desired wall thickness is obtained, with selected and variable orientations of the fibers in the plies. Small inserts, illustrated at 16, often are included as reinforcing plies, usually at the ends of the shaft, all in accordance with conventional industry practices.

Material is applied to the mandrel using various well known techniques, using precut patterns of composite material that are applied in prearranged layers. The materials used can be selected from a wide range of composite fibers, including, but not limited to, pan-based carbon, pitch-based carbon, fiberglass fibers, aramid fibers such as Kevlar or Zylon, and a variety of ceramic fibers. The resins are selected from a variety of thermoset or thermoplastic resins to form a fiber-reinforced composite material in tape or sheet form. Material selection is based upon desired criteria that pertain to shaft characteristics of flex, weight, torque and strength, and possibly others, all well known to those skilled in the art.

In accordance with the present invention, the golf club shaft 10 is produced in two separate segments, a tip section 17 and a butt section 18, that are separately wrapped onto a mandrel 19, the smaller tip section first, followed by the larger, overlapping butt section. Formed in this manner, the two sections can be independently designed to have plies 20 and 21 that produce the performance characteristics that are desired, and are separately wrapped and joined securely together by their overlapping end portions.

The type of mandrel 19 for use in practicing the invention is illustrated in FIG. 4 as having a discrete or pronounced step 22 at the end of its smaller end portion 23 on which the tip section 17 is wrapped. The tip section is produced on the smaller end of the mandrel, with the outer ply 20 substantially level with the surface of the larger mandrel portion 24, and the butt section 18 then is wrapped onto the larger end portion of the mandrel. A short overlapping portion of the butt section, indicated at 25, extends over the adjacent end portion of the tip section 17, to join the two sections together. Conventional reinforcing wraps may be included, as illustrated at 26 in FIG. 4.

It is to be understood that the longitudinally compressed and exaggerated step 22 shown schematically in the drawings actually is longer and more gradual. A typical step will extend over a length of several inches, with the ends of the plies graduated longitudinally to lie along the incline of the step. The length of the overlap 25 of the two sections 17 and 18 may be varied in different shafts, but should be long enough to ensure secure joinder of the sections but not so long as to produce an objectionably long section of the increased stiffness that results from the combined wraps of the butt and tip sections. A preferred length of overlap is in the range of four to six inches in the illustrative shaft, and a practical maximum range should be approximately one to eight inches.

This method of producing the shaft 10 makes possible the production of the shaft with different selected combinations of butt-section and tip-section characteristics for optimized overall performance of the shaft. In accordance with another aspect of the invention, a selection of at least two different tip sections 17 having different predetermined stiffness characteristics is provided, along with a selection of at least two different butt sections 18 having different predetermined flex characteristics, and shafts are produced with different combinations of selected tip and butt section characteristics to provide a shaft with optimized performance characteristics for a particular swing. Preferably, butt sections are provided in at least two weights and three different flexes for each weight, and tip sections are provided in three different stiffnesses for each weight, thereby providing a wide variety of choices and combinations.

These combinations can be made available to the trade and will provide a wide range of performance characteristics from which a selection can be made to suit a particular golfer's swing.

The table shown in FIG. 9 shows an example of the possible combinations of tip section and butt section that can be made available when three different tip section stiffnesses and three different butt section flexes are made available in two different shaft weights, namely, a sixty-five gram weight (approximate) and an eighty-five gram weight. The three different flexes ae shown in the table as “R” (regular), “S” (stiff) and “X” (extra stiff) and the tip flexes are shown as “Low Launch” (high stiffness), “Mid Launch” (medium stiffness) and “High Launch” (soft), all of these being terms that are known and used in the golf club industry.

Under the headings indicating three ranges of speed of the golfer's swing are figures indicating the approximate amount of carry for a well-hit shot, and under each speed range is a “Desired Launch Angle” that indicates the flex of the shaft (“R”, “S” or “X”) that should be combined with the particular tip section (“Low Launch”, “Mid Launch” or “High Launch”), indicated along the left margin of the table. The designations “65” and “85” are weight categories.

The top portion of the table contains exemplary tip diameters (two being offered, for different heads), butt diameters, torque, weight and length of a representative shaft design. The “−3” designation on the length indicates the length of the end portion that is untapered for insertion in the club head. It is to be understood that these figures are for purposes of illustrating one possible embodiment of the invention, for an illustrative wood, and are not to be taken as limiting in any way. Further, it is to be understood that those skilled in the art of designing and producing conventional composite golf clubs are aware of the factors that determine performance in conventional clubs of the type illustrated in FIG. 3, and will be able to apply those factors in producing flex-segmented golf clubs in accordance with the invention as described herein.

The shafts thus formed have a pronounced, discrete and visible external step 30 in the external surface of the shaft between the butt section 18 and the tip section 17. As shown in FIG. 4, this step initially will be shaped by the edges of the plies 21 that have been wrapped on the mandrel, and then may be pressed and shaped to a different configuration during the curing of the shaft, whether by molding or by other well known means. Possible profiles for the step 30 are shown in FIGS. 5A to 5D, as a sharp ninety-degree step 30 a, normal to the shaft axis (FIG. 5A), a tapered step 30 b (FIG. 5B), a convexly rounded or “bull nose” step 30 c (FIG. 5C), or a concavely rounded step 30 d (FIG. 5D). These are all matters of aesthetic appearance rather than functional utility.

Shown in FIGS. 7 and 8 is a representative layup arrangement, indicating the manner of applying at least two plies 20 and at least two plies 21, along with two representative reinforcing plies 26 and 31. The positions along the mandrel 19 are indicative of the longitudinal positioning of the wraps, and the spacings outwardly from the mandrel are indicative of the order of application. The plies 20 are applied first to the smaller portion 23 of the mandrel, as shown in FIG. 8A, and the plies 21 then are applied to the larger portion 24 of the mandrel, as shown in FIG. 8B.

The amount of overlap (25 in FIG. 4) is determined by the length of each ply 20, 21 and its placement on the mandrel 19, as can be seen in FIG. 5. This overlap may be varied with the particular shaft type and construction that is being produced, and in any event is long enough to join the sections securely together. For the illustrative example referred to in FIG. 9, in which the shaft is forty-six inches long, the plies 20 (of which there may be more than two) may be, for example, from about twelve inches long to about twenty inches long and the plies 21 may be about thirty-three inches long. Inserts and reinforcing plies are optional and their placement and dimensions are a matter of choice.

Description of the Alternative Embodiment

Shown in FIG. 6 is an alternative embodiment of the invention in which the butt section 18 of the shaft 31 is formed as two pieces, an intermediate or transitional section 18 a and an extension or end section 18 b. The tip section 17 remains the same as in the first embodiment, and the first step 30 in the external profile remains the same, but the plies 21 a forming the intermediate section are shortened and wrapped on an intermediate portion 23 a of the modified mandrel 32, up to an intermediate step 33 in the mandrel, and the extension section 18 a is formed by additional plies 21 b wrapped on the end section 23 b of the mandrel, forming a second external step 30 a in the shaft. A shaft in accordance with this embodiment of the invention may have sections of varying length. This embodiment otherwise is the same as the first embodiment, but provides the capability of further customized shaft characteristics in the intermediate section 18 a.

From the foregoing, it will be evident that the present invention provides a golf club shaft that may have optimized performance characteristics matched to a particular golf swing in a novel and highly effective fashion. It also will be evident that, while two embodiments have been illustrated and described, various modifications may be made by those skilled in the art within the scope of the invention. 

1. The method of producing a golf club shaft made up of a butt section and a tip section having optimized performance characteristics for a particular golf swing, comprising the steps of: providing a selection of at least two different tip sections for said shaft having different predetermined stiffness characteristics; providing a selection of at least two different butt sections for said golf shaft having different predetermined flex characteristics; producing a selected one of said tip sections as a separate segment having at one end portion for connection to a club head and a second end portion for connection to a butt section; and producing a selected one of said butt sections as a separate part having one end portion disposed around and overlapping with the selected tip section and securely joined thereto, whereby the resulting shaft has performance characteristics determined by the combination of the selected tip section and the selected butt section.
 2. The method defined in claim 1 wherein said steps of producing the selected butt section and the selected tip section are performed by wrapping composite material on a mandrel having tip and butt end portions of smaller and larger sizes, respectively, joined by a discrete step and designed to produce the selected tip and butt sections of the shaft, the selected tip section being wrapped on the smaller end portion of the mandrel with said one end portion against said discrete step and the selected butt section being wrapped on the larger end portion of the mandrel and extending a predetermined distance beyond said step to overlap said one end portion of the tip section.
 3. The method defined in claim 1 wherein said selection of tip sections comprises tip sections having at least three different stiffness characteristics and said selection of butt sections comprises butt sections having at least three different flex characteristics.
 4. The method defined in claim 3 wherein said different tip sections have stiffness characteristics for low launch, mid launch and high launch, and said different butt sections have flex characteristics that are low, medium and high flexes.
 5. The method defined in claim 3 wherein each of said selections comprises different tip sections and different butt sections for at least two different weights of club for each selected combination.
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 13. A flex-segmented golf club shaft having tip and butt sections, comprising: an elongated tip section of predetermined length and preselected stiffness characteristics composed of composite material and having one end portion for connection to a golf club head and a second end portion for connection to the butt section; an elongated butt section composed of composite material and having one end portion disposed around and overlapping said second end portion of said tip section and securely joined thereto and having preselected flex characteristics; and a step in the outside surface of said shaft at the end of said one end portion of said butt section; said butt and tip sections being separate pieces joined together by the overlapping end portions whereby each section may be designed for optimized performance characteristics for a particular golf swing.
 14. A flex-segmented golf club shaft as defined in claim 13 wherein said tip section and said butt section are tubular composite parts, the outside diameter of said second end portion of said tip section and the inside diameter of said one end portion of said butt section being the same and being fused together.
 15. A flex-segmented golf club shaft as defined in claim 13 wherein said butt section overlaps said tip section by a preselected distance sufficient to join the sections securely together without interfering with the flexibility of the shaft.
 16. A flex-segmented golf club shaft as defined in claim 15 wherein said preselected distance is in the range of approximately four inches to approximately six inches.
 17. A flex-segmented golf club shaft as defined in claim 15 wherein said preselected distance is between a minimum of one inch and a maximum of eight inches.
 18. A flex-segmented golf club shaft as defined in claim 13 wherein said butt section comprises an intermediate section joined to said tip section and an end section overlapping and joined to said intermediate section.
 19. A flex-segmented golf club shaft as defined in claim 13 wherein said step in the outside surface has a preselected contour selected from the group comprising a shoulder normal to the shaft axis, a taper, concavely rounded, and convexly rounded. 